A field harrow's performance can be tuned to the conditions the user faces by adjusting the tine angle to change the aggressiveness of the harrow tines. Typically the harrow comprises a plurality of harrow sections supported along the length of a tool bar. Each harrow section consists of several bars spaced apart and each has several harrow tines mounted to it. The bars of each harrow section are linked together with a link arm of that section. The control of the link arm is typically controlled either independently of the other harrow sections using hydraulics, or the link arms are linked together using a rockshaft spanning the width of the sections.
Examples of a rockshaft linking the harrow sections can be found in U.S. Pat. Nos. 5,492,182 and 6,164,386 by Delaurier. While this configuration is suitable for linking the rotation of the tine angles for common tine angle adjustment, differences in ground contour can result in some tines engaging the ground with greater pressure than other sections so that the harrowing action may not be even regardless of the tine angle being maintained the same throughout the implement.
Alternatively, common tine angle adjust can be accomplished by using phasing cylinders linked in series. Use of hydraulics can more evenly distribute the ground engaging force among the tines, but traditional use of phasing cylinders generally require a complex arrangement of parts. Phasing cylinders work by connecting one port of each cylinder to an alternating port of the next cylinder in the series. Oil is forced into the first cylinder on one side of the piston. As the cylinder rod and piston are moving from the added oil, it is also displacing oil out the top port being forced out from the piston. This volume however is not equal to the same amount of oil entering the cylinder on the bottom side of the cylinder due to the fact there is a cylinder rod on the top end and thus a smaller surface area of the piston causing a decrease in oil output. While the first cylinder's top port is connected to the second cylinder's bottom port, the second cylinder's cross section will need to match that of the first cylinders piston minus the cross section area of the rod to produce the same amount of stroke. This series can include as many cylinders as desired, as long as they are all sized differently in a proper sequence. An illustration of a typical series of master and slave cylinders in a phasing relationship is shown in FIG. 1 in which the area about the piston rod of the piston is equal to the area of the cylinder end of the next cylinder to which it is connected so that the cylinders are displaced simultaneously with one another. A large implement with many cylinders in series results in costly maintenance as each cylinder is different in size and configuration so that each cylinder requires its own dedicated replacement parts.
Various examples of hydraulic circuits are described in U.S. Pat. No. 7,478,683 by Peck et al, U.S. Pat. No. 5,449,042 by Landphair et al, and U.S. Pat. No. 4,335,894 by Swanson; however, none are well suited for use in a harrow for controlling tine angle in an efficient manner as conventional rotary rephasing valves and other conventional rephasing techniques are used.